Wow! Thank you very much for this very detailed comment!
You made lots of pertinent suggestions, and I apologize for the most aproximation of the patterns of each boss, it was very hard to program and often I was content with what worked without trying to get the best.
For the graphics of the game, I did everything during the jam, I don't really have the means to prove it, but I posted on a discord server some screenshoots on the progress of the project (with the date)
For the theme, I work around the returned cross and the beyond, but it is more a design and lore choice for the game more than the mechanics. ^^;
Thank you again for your feedback, and I'm very glad you liked the game :)